In recent years, microparticles are being used widely in industrial fields including an optical material, a magnetic material, a conductive material, an electronic material, a functional ceramic material, a fluorescent material, a catalyst material, and a chemical material. As the requirements for multifunction and downsizing in products increase, there are needs to incorporate functions therein as many as possible, and in addition, to realize further downsizing and lightening in its weight than ever before. In order to meet these needs, microparticles of the various above-mentioned materials are wanted. Besides, by transforming these materials to microparticles, the microparticles thereby obtained may acquire new physical properties such as higher activity and higher transparency.
On the other hand, in an electronic material, a magnetic material, an optical material, a heat-resistant material, a reinforcing material, a fluorescent material, a catalyst material, and a chemical material, an alloy microparticle comprising plural metal elements and a composite metal compound microparticle such as a composite metal oxide microparticle have been used; and moreover, in order to meet the diversity in their uses and performances, various composite microparticles have been proposed.
General production methods of alloy microparticles are classified roughly into a solid phase method, a gas phase method, and a liquid phase method. In the solid phase method, heat treatment at high temperature for long treatment time is necessary, and in the gas phase method, capital investment on the equipment and running cost thereof are large; and thus, naturally alloy microparticles obtained and the products obtained by using the said alloy microparticles tend to be expensive. In separation of an alloy microparticle by a coprecipitation method as shown in Patent Document 1, which is one of the liquid phase method, different behaviors of each metal element in the solution, such as diffusion of each of the metal elements in the solution in which different metals or metal compounds which are raw materials of the microparticles are contained, cannot be neglected so that to control the molar ratio between different metal elements that constitute the alloy microparticle is difficult; and as a result, to obtain the homogeneous microparticle thereof has been difficult. Accordingly, in the method for production of the alloy microparticle by the conventional liquid phase method, metal elements that can be used are limited; and thus, there have been problems that combination of metal elements as well as the ratio thereof could not be selected freely.
In addition, the method as shown in Patent Document 2 in which a liquid or a slurry that contains inorganic metal compounds is dried by contacting it with a high temperature pulse burning gas requires an equipment to generate the pulse burning gas; and thus, there have been problems of high energy cost etc.
A method for producing nanoparticles using a rotation processing method with a forced ultrathin film as shown in Patent Document 3 filed by the applicant of the present invention has been disclosed; however, undisclosed therein was the specific method to control circumferential speed of the rotation at the converging point of at least two fluids to be processed between at least two processing surfaces thereby controlling the molar ratio between different metal elements in the composite microparticle that is separated in a thin film fluid formed between the processing surfaces which are disposed in a position they are faced with each other so as to be able to approach to and separate from each other, at least one of which rotates relative to the other. Accordingly, a method for producing an alloy microparticle or a composite metal compound microparticle containing different metal elements whose molar ratio is controlled has been eagerly wanted.